The objective of this proposed study is to continue to investigate those factors which regulate the reversible inactivation and reactivation of kidney adenosine triphosphatase (ATPase). It is believed that the inactivating and reactivating systems are distinct from ATPase. The data has revealed that (Na ion plus K ion)-ATPase can be reversibly inactivated. Inactivation is mediated by a cyclic AMP dependent protein kinase. Reactivation is mediated by a soluble factor in the 100,000 xg cell supernatant fraction. The component required for the 'reactivation' of inactivated ATPase will be purified by methods similar to those utilized in the purification of ATPase. The reactivating factor will be assayed by its ability to reactivate ATPase entrapped with protein kinase in artificial liposomes, or by an alternate assay. Once the factor is identified and purified, it will be utilized to further characterize in inactivating component (cyclic AMP) dependent kinase and for reconstitution studies. The kidney ATPase is purified from human kidney. Certain studies may also be continued with the rat kidney enzymes.